The present invention relates to an antenna transducer comprising, in series from an access intended to be coupled to the radiating part of an antenna, a first polarizing duplexer for working in a first frequency band, a transition element formed from a variable-section guide and a second polarizing duplexer for working in a second frequency band.
The use of such antenna transducers for allowing an antenna to operate with great polarizing purity is known; the two frequency bands of these transducers are respectively a low-band for the working frequencies of the first polarizing duplexer and a high-band for the working frequencies of the second polarizing duplexer. These known transducers have their first polarizing duplexer which comprises four lateral polarizing accesses spaced apart by 90.degree. from each other and the separation between the frequencies of the two bands takes place by means, on the one hand, of high-pass filters situated in the transition element and/or in the second polarizing duplexer and, on the other hand, low-pass filters placed in the lateral waveguides ending at the four lateral accesses of the first polarizing duplexer. The filters used in these known antenna transducers are filters with two or three cavities, adjustable by means of plungers, i.e. rods capable of being inserted to a greater or lesser extent in the cavities. Such antenna transducers present different drawbacks:
they are expensive because of the filters which they use, PA1 their transmitting and receiving passbands are relatively small, PA1 resonance phenomena tend to occur in the high-frequency band, i.e. in the working frequency band of the second polarizing duplexer.
The present invention aims at considerably reducing the above drawbacks.